1. Field of the Invention
The present invention relates to an apparatus making it possible to measure the position of a moving member, such as a bar, relative to a fixed member, such as a cylindrical enclosure in which the said bar moves.
Such an apparatus is more particularly used in the measurement of the position of absorbing control rods, which make it possible to check the reactivity in the core of nuclear reactors of any random type (pressurized water, boiling water or fast neutron). However, the present invention is not limited to this application and can be used in all cases where it is necessary to accurately know the position of a member moving in a given direction, even in a hostile environment and without the overall dimensions of the apparatus becoming excessive.
2. Description of the Prior Art
In the present state of the art, the detection of the displacement of control rods in the core of 900 MW pressurized water reactors is carried out by means of a differential transformer. However, this detector type has an inadequate resolution (1/30 of the total travel of the rods, i.e. 123 mm for a travel of 3700 mm). Moreover, there can be no more than one detector per mechanism.
These limitations, which were not fundamentally disturbing for such a reactor type, become highly prejudicial in the case of certain nuclear reactor projects, in which the optimization of the operating conditions lead to a very accurate check of the position of the absorbing rods in the core and confers on this measurement safety conditions implying redundant measures on each of the inspection mechanisms.